If you HAVE to stay SBP it might be much cheaper (and better in the long run) to just get new axles in SBP for the 8 1/4. They must exist. The upgrade to the 8 1/4 is definitely worth it.
For city/highway gears. 3.23 or 3.55. In my mind 3.55 has always kind of been the ultimate "compromise" gears. It works good on the street and highway.